Re: [patch] document that O_TMPFILE works with shm_open

[Florian Weimer <fw-d32yF4oPJVt0XxTmqZlbVQ@public.gmane.org>]

* Daniel Colascione:

> On 10/27/2015 03:12 PM, Florian Weimer wrote:
>> * Daniel Colascione:
>>
>>> This test program works fine. (Watch it work in strace.) This patch is
>>> against git master. It's okay to document accidental features, right?
>>>
>>> int
>>> main()
>>> {
>>>     int shmfd = shm_open(".", O_TMPFILE | O_RDWR | O_EXCL, 0600);
>>>     ftruncate(shmfd, 1000);
>>>     mmap(NULL, 1000, PROT_READ | PROT_WRITE, MAP_SHARED, shmfd, 0);
>>>
>>>     return 0;
>>> }
>>
>> This looks more like a bug to me.  I wouldn't count on it continuing
>> to work.  glibc already tightened the rules for the name once.
>
> I don't think they can break compatibility like that, and besides: it's
> a useful feature, not a bug.

Names not starting with '/' do not have well-defined behavior with
shm_open.  Applications shouldn't rely on that.

> Is it better for people to blindly open files in /dev/shm? Because
> that's what they do today.

memfd_create is the official interface for this purpose.  But neither
O_TMPFILE or memfd_create is very widely supported.

Florian
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